Grass seed calculator
Pick your grass type and lawn size — get pounds of seed at correct extension-service rates, and the bag count to buy.
Result
Grass seed needed
How much grass seed do I need?
Formula
lb = lawn ft² × rate (lb per 1,000 ft²) ÷ 1,000 · bags = lb ÷ bag size
Example: a 50 × 20 ft lawn (1,000 ft²) seeded new with tall fescue (9 lb/1k): 9 lb = two 5 lb bags. Overseeding the same lawn with bluegrass: 1.25 lb — one 3 lb bag does it with leftover.
Why rates differ so much
Bluegrass seed is tiny (~2M seeds/lb) — a little goes far but it's slow. Fescue and rye seeds are large: more pounds per area, but they sprout in days. That's why "one rate for all seed" packaging advice is usually wrong; extension rates (used here) run:
| Grass | New lawn | Overseed |
|---|---|---|
| Kentucky bluegrass | 2–3 lb/1,000 ft² | 1–1.5 |
| Tall fescue | 8–10 | 4–5 |
| Perennial ryegrass | 5–6 | 2.5–3.5 |
| Fine fescue | 4–5 | 2–3 |
Seed lasts; cheap seed doesn't
Read the tag before the bag. Look for weed seed <0.5%, no "other crop" above 0.5%, germination ≥85%, and a test date within 12 months. "Contractor mix" at half price usually contains annual rye that dies the first winter. Seed kept cool and dry stays viable 2–3 years.
For the layer underneath: topsoil calculator — new lawns want 4–6 in of root zone.
Frequently asked questions
How much grass seed for 5,000 square feet?
Tall fescue new lawn: 45 lb (one 50 lb bag). Bluegrass new lawn: 12.5 lb. Overseed at roughly half these.
Can I put down too much grass seed?
Yes — above ~1.5× the rate, seedlings crowd and damp off (fungal kill). Follow the rates in the dropdown, not the bag's marketing.
How much seed do I need to overseed?
About half the new-lawn rate — pick the "overseed" options in the dropdown. Best windows: late summer/early fall for cool-season grasses.
How do I calculate seed for an odd-shaped lawn?
Use the Known area tab with your best ft² estimate (pace it: one long step ≈ 3 ft), or break into rectangles and add.
Is a 50 lb bag of seed too much for a small yard?
For under ~2,500 ft² of fescue, yes. Buy smaller bags — or go in with a neighbor; sealed seed keeps 2–3 years at most.